Lead compensated sight



33"233a (JR 793869262 55R Oct. 9, 1945. REIERSQN 2,386,262

LEAD COMPENSATED SIGHT Filed May 6, 1943 2 Sheets-Sheet 1 IJE, I JnhnE.-HeiE1-'5c|n' 33. GED M ETRI CM. IN 3 RU M H! ES, 1::

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LEAD COMPENSATED SIGHT Filed May 6, 1943 2 Sheets-Sheet 2 i I I D j Juhn ElReiere on u maammnwu 33. GEUIVIEI HIUAL INISHiUMtNISI Patented Oct. 9, 1945 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) Claims.

The invention decribed herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to fire control devices, more particularly, to such devices which are designed to be incorporated with the sights of a gun, such as a machine gun. The prime object of the invention is to devise a fire-control gun sight which will automatically compensate for lead, especially in the case of a moving target. For the attainment of this and such other objects of invention as may herein appear or be pointed out, I have shown one embodiment of my invention in the accompanying drawings, wherein:

Fig. l is a perspective view of a field of fire divided into stadia points and showing other particulars referred to in the specification;

Fig. 2 is a graph depicting a number of plotted lead curves referred to in the specification;

Fig. 3 is a perspective view of the improved fire control sight applied to a machine gun.

Fig. 4 is a perspective view showing a gun in firing position and equipped with the improved sight; and

Fig. 5 is a. front view of a modified form of slide arrangement.

Before describing the device of this invention certain characteristics of exterior ballistics and fire control bearing upon the invention will be pointed out, together with an original manner of considering such factors as target position, future position, present position, leads, etc. For facility in exposition and illustration, we take as example the case of a target moving at a constant speed in a rectilinear path and at a constant altitude. The target path is represented in Fig. 1 by the horizontal lines Ha -H1. H in e accepted military symbol for altitude; the subscript R and L indicating a point to the right and left, respectively, of the midpoint M; and the superscript 600 indicating an altitude of 600 yards. The target path is, as premised, at a constant altitude above the ground line HR-HL. As is usual in fire control problems, a horizontal line GM through the gun G normal to the field of fire (plane HL -HL-HR-HR intersects the midpoint M; the line GMO is the minimum horizontal range (to target at midpoint of course) and is symbolized Rm. By way of example a field of fire or target course 1000 yards from G is taken, ie., Rm=1,000.

The system of this invention contemplates dividing the field of fire, Fig. 1 by a plurality of vertical planes parallel to the minimum horizontal range Rm and equi-distant from one another a predetermined distance, such as 500 yards. The plurality of planes, which might be termed stadia planes, intersect the target path in a plurality of equi-spaced stadia points. Nine such stadia planes are comprehended in Fig. 1, resulting in nine stadia points as shown in the figure, numbered l, l etc. up to 5, the midpoint M being stadia point 3. The stadia points are numbered from right to left because the target is assumed to travel in that direction. Each of the stadia points is assumed to represent the predicted (future) position of target, symbolized Tp. The stadia points are thus identified as Tpl, T m etc. While the expression predicted (future) position of target is accepted military terminology, this position will be referred to by the expression future hitting position, which is more apt for reasons subsequently apparent. The future hitting positions, symbolically represented by small squares, represent points or positions where the projectile fired from gun G meets or "hits the target coming from a correlated present target position. The latter positions are herein renamed calculated firing positions as a more apt expression because such position is calculated from predetermined future hitting position and is the position of the target at the time of firing the gun. Calculated firing positions are symbolized in accordance with military usages, To, and are schematically shown in Fig. 1 by a small circle, only T02 being shown.

The calculated firing position of, say, T02 corresponding to a future hitting position Tp2 is readily calculated from the known factors above assumed, viz., Rm=1,000, H=600 and a distance of the future hitting-stadia position from the midpoint M of the course (symbolized, Lp) equal to 1,000 yds. (since stadia point #2 is two stadia positions, each 500 yds., from M), and a given target speed, say an aeroplane at miles per hour (symbolized as Sg, or ground speed of target, since target path HR HL is horizontal, Fig. 1). Knowing Rm, H and lap, the distance GTp from gun G to the target at future hittingstadia point Tpz (i. e., the slant range, symbolized D) is calculated. However, the slant range D is used in entering the firing tables to determine the time of flight of the projectile of specified characteristics fired from a given armament, only in the case of a target at, or substantially at, the horizontal plane through the gun site (H=0). To determine the projectile time of flight in the case, as shown in Fig. 1, of a target, at a considerable altitude, such as H=600, the proper firing tables (generally, for anti-aircraft use) is entered with H600 and R the horizontal range to target at future hitting position Tp. By multiplying the 8g (in yds. per sec.) by the time of flight (t, in sec.) the distance of target travel T02Tp2 may be determined and the calculated firing position T02 fixed. The calculated firing positions T0 corresponding to all the stadia points (future hitting positions) are similarly calculated. a

It is next required to determine the lead, both lateral lead (symbolized, 5L) and total vertical lead (O'L). Lateral lead 51. is the angle subtended (in the slant plane) at G by the target travel To Tp due to the motion of the target during the time that the projectile is in flight. Total vertical lead at is comprised of two factors, the change in the vertical deflection angles at T0 and T 0 and the superelevation, s, occasioned by the trajectory form of the projectile. The vertical deflection angle at point T02 is designated 0'0 in Fig. 1 while the corresponding angle at point T is designated Up. The change in vertical lead due to change in vertical deflection angle as the target progresses from T0 to T is 0 The value of a a0 may be either (i. e., an increase in vertical lead upward) or it may be (i. e., a dcrease in vertical lead, or lowering of the gun muzzle). The comparative values of deflection angles (Io-O' and the sense of their algebraic summation (0'p00) are readily discernible by considering the trigometric relation between H (identical at T and T0 since the target wanes at constant altitude, H =600) and the horizontal range, respectively, Rp and R0, since 7 the deflection angle a is tan- H+R. Since H is constant, only the value of R need be considered. In the case of the target moving rightwardly from T02 to T02, Fig. l, the value of R0 is greater than R Hence 17p will be larger than 00, and the algebraic total (o' o'u) will be indicating increasing (upward) lead as the target approaches midpoint M.

The lateral lead (61.) and vertical lead are determined for all the stadia points (Tp and correlated T0), 1. e., for the nine points shown in the example of Fig. 1. The values of such leads (6L and 01.) in angular mils are plotted in Fig. 2 with lateral lead (61.) as abscissa and vertical lead (17L) as ordinate or elevated vertical lead being above the abscissa, and or lowered vertical lead being below the abscissa). Curve A represents the leads in the case of the example taken, namely, a right-to-left moving target, constant speed Sg=120 mi./hr., at H=600 in a plane at Rm=1,000, for a given armament (gun and ammunition). Lateral lead always leads, or is forward of, a moving target (its magnitude either increasing or decreasing). In the case of a target moving from right to leftas in the example-lateral lead will always be to the left of the target; we will arbitrarily consider left-ahead lead as and plot such lead to the right as the ordinate, as has been done in the case of curve A.

The numbered marks (I, 1 /2, 2 etc.) on curve A correspond to the stadia points of Fig. 1 and represent the actual value of the lead (61. and in.) in mils required for hitting the target at the respective stadia points, i. e., at the future hitting positions Tp. For example, point I of curve A reveals that, to hit the target at Tpl'WheIl. the target is sighted at T01 (not shown in Fig. 1)

the gun is required to be given 6L of 9 mils and an of 23 mils. As shown in Fig. 1, hitting position T 1 is 2,000 yds. to the right of midpoint M. Point I /2 of curve A reveals that an increased 51. of 10 mils and a decreased an of 19 mils are required, etc.

Curve A is used in preparing a sight slide l0, Fig. 3, of Celluloid or other suitable transparent material which is held in a frame 20 secured at the muzzle end of the gun, to the cooling jacket I of the machine gun and replaces the front sight of the gun. The curve of sight slide [0 corresponding to curve A of the graph of Fig. 2 is designated A". One outstanding difference between the sight slide curve A" and its counterpart curve A is that the two are exact mirrorreverse on the abscissa. A mirror-reverse" curve of curve A or the graph is shown in Fig. 2 and there designated A. The reason for mirrorreversing (on abscissa, or in a vertical sense) curve A for incorporation in the sight slide as curve A" will be explained with the aid of Fig. 4. The sight plate I0 (corresponding to the sight ID of Fig. 3) is secured at the muzzle end of cooling jacket I. The center 0' of sightplate ID, at the intersection of the horizontal reticle h-h and the vertical reticle vv, correspond to the origin 0 of the graph of Fig. 2. In Fig. 4 the gun is laid to hit a target at stadia point 2 (future hitting position Tp2), the target being at the time of firing at calculated firing position T02. That is, at the time of firing the target is sighted at T02. By this statement it is meant that the target (T02) and the rear sight 9 are on a line which passes through the point-point 2on curve A" which corresponds to the stadia point at which the target is sighted. Referring to the graph of Fig. 2 it will be seen that point 2 of curve A, by reason of the manner of constructing the curve as explained above, is above the abscissa axis. If curve A were used directly in the sight plate it will be apparent, to align the said line of sight (rear sight to T02) with point 2 of the curve, that the gun would be depressed rather than elevated as it should be, to hit an elevated target (such as aircraft flying at H600, as in the example). Hence point 2 on the sight plate curve A, Fig. 2 should be below the abscissa axis the precise distance that point 2 of the plotted lead curve A is above the abscissa axis. Similarly with the other points of the curve; i. e., curve A, see Fig. 2, is a mirror-reverse of curve A about the abscissa axis.

The curve A" of the sight plate is precisely geometrically similar to the inverted plotted lead curve A of the chart of Fig. 2, but is considerably smaller. The actual size of sight curve A" will depend upon the dimensions of the sight frame and, particularly, the distance between the sight plate and the rear sight.

The manner of operation should be clear from the foregoing description, especially the explanation of Fig. 4. The gunner sights the improved device by adjusting the gun, both in azimuth and in elevation, so that the line of sight (from the rear sight to the target, see Fig. 4) passes through the point of the sight curve numbered in correspondence with the stadia number of the targets course, more articularly the future hitting position Tp. As clearly shown in Fig. 4, the line of sight contains the point on curve A" point #2- which corresponds to the position (i. e., the calculated firing or present position) of the target shown-T02 correlated to stadia poi t (a T112) Of course, the gunner must know the stadia num- 33. GEOMETRICM. YNSWUMENTS.

ber of the target and is usually given this information by a director station or other observer. As the target continues on its course (leftward in the example taken) from 2 to 2 3, etc., the gunner adjusts the gun, keeping the line of sight on the proper stadia points of the curve, so that the muzzle end of the gun traverses a path corresponding in appearance to that of the sight curve. The gun is so moved that the target appears to be touching and moving along the curve at the proper rate. The proper rate is such that when the target is at a certain present (To) On its course it will appear to be at the corresponding position on the curve.

It was premised above that the target moves from right to left. A imilar shaped curve (B and B in the chart of Fig. 2 and B" in Fig. 3) is prepared for a target moving in the opposite direction, from left to right. It will be seen, as by comparing the right-to-left curve A of Fig. 2 with the left-to-right curve B, that the two curves are mirror-reverses on the vertical ordinate axis. This is also true of the other corresponding curves, A and B, and A" and B". As previously described the stadia points in the case of a rightto-left target (such as shown in Fig. 1) are numbered consecutively from right to left. The stadia points are numbered, from 1, 1%, 2 etc. up to 5, from left to right (although not shown in figure) for left-to-right targets.

It was also premised above that the curve (A in the case of a right-to-left target, and B in the case of a left-to-right target) is based upon the following factors: Sg=120 mi./hr.; Rm:1,000 yds; H=1,000 yards. The sight curve plate or pellicle contains curves applicable to targets and target courses the value of whose Sg, Rm, and H factors are different from those enumerated above. As an example, a series of curves are shown in the chart of Fig. 2 and in Fig. 3, in which one of the three factors, more particularly, Sg, has been varied, with the other factors remaining, Rm at 1,000 and H at 600. The said series of speed curves include, in addition to curve A (or A) having Sq 120, curve A (or A2) based upon a S; value of 140', and A3 (or A3) based upon a Sg value of 160. Which one of the three curves (A", A2", and As", Fig. 3) the gunner would use depends upon the speed of the target. To facilitate the operation of keeping the line of sight passed through the proper one of the set of speed curves, the curves may be differently or contrastingly colored.

Each sight curve corresponds to a certain course and target speed: therefore the curve which more nearly corresponds to the targets course and speed is chosen, and if it isnt quite correct an imaginary curve is used. A better way is to use an actual curve and correct its shape and size by means of a flexible rear sight which is capable of being moved laterally and verti-- cally.

The distances between adjacent present positions on the course are nearly equal and the times for the target to fly these intervals are about equal. The times between points on the course and therefore between points on the curve are nearly equal. The distances between points on curves are directly proportional to the angular travel of the target, for example: on course A (curve A") the distance traversed by the target going from In to 20 is about the same as from the latter to 30, but the angular travel between the former is much less than in the latter. The ratio can be seen on curve A when distance l 2 is much less than 2-3. The latter fact is an aid to the gunner in pointing. He has the job of moving the gun so that the point on the curve will be on the target when the target arrives at that present position on the course, for example: Point 2 on curve A" is aligned on the target at which time the target is at the present position or calculated firing position T02 and the gun is pointing at the future position or future hitting position Tp2. From point 2 on the curve, the gun is moved so that the target appears to move along (and tangent to) the curve at such a rate that it will arrive at point 2 on the curve when the target arrives at point T02; on the course.

The sight plate ll) of the device may comprise a single set of curves (such as the set of rightto-left curves A and the left-to-right curves B, at various speeds) or it may comprise a number of panels, such as are indicated in Fig. 3, which may be brought into operative position (by centering on a pointer 2| on the center line of the gun) by moving the plate [0 relative to its holder 20 and secured in position, as by wing nuts 22.

The sight curves may be arranged on a fiat plate, as shown in Fig. 3, or they may be arranged, individually or in panels each assigned to a particular set or family of curves, on a transparent film, e. g. acetate or Celluloid film, designated ll) in Fig. 5, which may be threaded through the gate 33 of the holder 20' secured on the cooling jacket. Film I0 is extended across the gate frame between a spool 34 at each side implemented with means, such as crank knobs 35, for advancing the film in either direction.

While the improved sight of this invention has been shown in the drawings as a transparent plate upon which the curve or curves have been engraved or otherwise marked, it is clear that the invention may be applied in other forms, as for exampleto describe but one other form the curve may be in the form of a wire or contoured plate (i. e., a plate cut to the contour or shape of the curve).

I claim:

1. A lead-compensated sight for aiming a gun at a target having straight-line, uniform speed in a particular one of a plurality of vertical planes representin field of fire which are equi-spaced from each other and normal to a line through the gun (the segments of the said normal line constituting the least horizontal ranges Rm of the respective planes), the space on both sides of the said normal line being divided parallel to the said normal by a plurality of vertical stadia planes equi-spaced from each other, the said plurality of stadia planes intersecting a horizontal datum plane through the gun in a plurality of parallel, equi-spaced stadia lines, and the stadia lines intersecting the said plurality of vertical planes representing fields of fire in stadia points, the said stadia points being numbered consecutively from right to left and from left to right to provide for motion of targets in either direction, the said sight comprising a pellicle holder mounted at the muzzle end of the gun in place of the usual front sight anda transparent, pellicle receivable in-thesaid holderar'idprovided with" sets of curves for predetermined conditions of target speed, altitudeand Rmvalue'feach curve being constructed by a fair curve through the plotted positions of the lateral and vertical leads pertaining to particular stadia points according to abscissa of lateral lead and ordinate of vertical lead, the said curve points bearing corresponding stadia numbers.

2. The combination according to claim 1 in which the said pellicle is in the form of slides and the said pellicle holder is a frame adapted to hold the said slides.

3. The combination according to claim 1 in which the said pellicle is in the form of aofilm and the said pellicle holder comprises a film gate disposed at the front sight, and a pair of spool holders adapted to position selected parts of the film in the said film gate.

a 1 ere, 

